This invention relates to circuit breakers such as molded-case circuit breakers and earth leakage breakers, and more particularly to power source means in an over-current trip section.
A circuit breaker is well known in the art in which its main circuit conductor has a U-shaped portion, and a Hall element is arranged as current detecting means between both legs of the U-shaped portion to detect current flowing in the remain circuit conductor (cf. Japanese Utility Patent Publication No. 26683/1993). The convention al circuit breaker is as shown in FIG. 4. As shown in FIG. 4, a current path is formed between a power-source side terminal 8 and a load side terminal 9 which comprises a switching section including a stationary contactor 10 and a movable contactor 11, a flexible conductor 11 whose one end is connected to the movable contactor 12, and a main circuit conductor connected to the other end of the flexible conductor 12. The terminals 8 and 9 are connected to external conductors with screws 13.
The movable contactor 11 is opened and closed with an operating section 14. The operating section 14 comprises an operating handle 15, a latch 16, a latch receiver 17, a toggle link 18, and an opening and closing spring 19. When, with the circuit breaker in "on" state as shown in FIG. 4, the operating handle 15 is moved to the right in FIG. 4, the toggle link is collapsed with the aid of the opening and closing spring 19, so that the movable contact 11 is disengaged from the stationary contactor 10; that is, the application of current is suspended. When an excessively large current (over-current) flows in the main circuit conductor 1, a trip coil (not shown) is activated, so that the latch 16 is disengaged from the latch receiver 17; that is, the latch 16 is turn counterclockwise about a supporting pin 20. As a result, the toggle link 18 is collapsed, and the movable contactor 11 is therefore disengaged from the stationary contactor; that is, the flow of current is suspended.
A part of the main circuit conductor 1 is U-shaped. Between the two legs of the U-shaped part of the main circuit conductor, a Hall element 3 for detecting current flowing in the main circuit conductor 1 is provided separately in each phase. The Hall element 3 is mounted on a printed circuit board on which an electronic circuit for the over-current trip section is formed. The main circuit conductor 1 and the printed circuit board 5 are accommodated in a casing 21. When a current I flows in the main circuit conductor 1, the portions of the U-shaped part of the conductor 1 produce magnetic flux outputs .phi..sub.1, .phi..sub.2 and .phi..sub.3 in the directions of the arrows. Inside the U-shaped part of the main circuit conductor, those magnetic flux outputs act on the Hall element 3 in the same direction. As a result, the Hall element produces a voltage (or Hall voltage) in a direction which is perpendicular to the directions of the current applied thereto in advance and the magnetic field. When the current I in the main circuit conductor 1 exceeds the rated value, then the Hall voltage also exceeds a predetermined value, as a result of which the electronic circuit applies a trip signal to the trip coil (not shown), so that the application of the current is interrupted.
In the circuit breaker shown in FIG. 4, a power source for the electronic circuit of the over-current trip section is obtained from the main circuit conductor. If, in the case where the power source is formed by a current transformer with the main circuit conductor as a primary conductor, it is intended to arrange the power source currents before and after the U-shaped part of the main circuit conductor, then the straight part of the main circuit conductor is unavoidably long, so that the resultant circuit breaker is elongated in the longitudinal direction as much. The power source current transformer of this type suffers from a problem that its output is insufficient in the case where the main circuit current is small.